There is known a suspension apparatus for use in a vehicle such that the suspension apparatus is provided between a body and four wheels of the vehicle. An example of an improved suspension apparatus is disclosed in, e.g., Japanese Patent Publication JP-A 11-510761.
The above-indicated Patent Publication discloses a conventional suspension apparatus in which a front-wheel-associated cylinder device and a rear-wheel-associated cylinder device are associated with each other by a first-chamber-associated passage, a second-chamber-associated passage, and a working fluid.
More specifically described, the front-wheel-associated cylinder device controls a relative displacement between the left and right front wheels in upward and downward directions of the body of the vehicle and, to this end, includes a housing and a piston fitted in the housing to divide an inner room of the housing into a first (e.g., an upper) fluid chamber and a second (e.g., a lower) fluid chamber.
Likewise, the rear-wheel-associated cylinder device controls a relative displacement between the left and right rear wheels in the upward and downward directions of the vehicle body and, to this end, includes a housing and a piston fitted in the housing to divide an inner room of the housing into a first fluid chamber and a second fluid chamber which correspond to the first and second fluid chambers of the front-wheel-associated cylinder device, respectively.
When the body of the vehicle rolls in one direction, respective pressures in the respective first fluid chambers of the front-wheel-associated and rear-wheel-associated cylinder devices change in a same direction, i.e., increase, or decrease. Likewise, when the vehicle body rolls in that direction, respective pressures in the respective second fluid chambers of the two cylinder devices change in a same direction, i.e., decrease, or increase.
The first-chamber-associated passage connects between the respective first fluid chambers of the front-wheel-associated and rear-wheel-associated cylinder devices and, likewise, the second-chamber-associated passage connects between the respective second fluid chambers of the two cylinder devices.
Thus, in the conventional suspension apparatus, the front-wheel-associated and rear-wheel-associated cylinder devices are connected to each other by the two passages, and the thus obtained pressure circuit is filled with the working fluid. The working fluid is preferably provided by a liquid that is incompressible in its natural state, but may be provided by a gas whose compressibility is considerably low, such as high-pressure gas.
When respective pressures in the two cylinder devices are substantially equal to each other, the working fluid is restrained from flowing between the two cylinder devices. Consequently the working fluid behaves as a rigid body, so that respective displacements of the respective pistons of the two cylinder devices are both restrained. This leads to improving not only a rolling rigidity of the vehicle body, but also a turning performance of the vehicle and the driver's steering feeling.
On the other hand, when respective pressures in the two cylinder devices are not equal to each other, the working fluid is allowed to flow between the two cylinder devices. Consequently the working fluid behaves as a soft body, so that the respective displacements of the respective pistons of the two cylinder devices are both allowed. This leads to improving articulation properties of the suspension apparatus, e.g., the property of allowing each wheel to displace quickly to follow irregularity of road surface, and the property of decreasing, when one of the left-side front and rear wheels, or one of the right-side front and rear wheels bounces, the change of sum of respective tread loads of all the wheels, or restraining the other wheel from bouncing. In addition, this leads to improving not only the driver's driving feelings, e.g., feeling of “flatness” and/or “heaviness” of the body when the vehicle is running, but also an off-road running performance of the vehicle.
Thus, the conventional suspension apparatus can automatically adjust the suspension properties of the vehicle. However, generally, every industrial product is desired to have a higher reliability.